Seed predation, often referred to as granivory, is a type of plant-animal interaction in which granivores (seed predators) feed on the seeds A seed ( /ˈsiːd/ ) is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant. The formation of the seed completes the process of reproduction in seed of plants Plants are living organisms belonging to the kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The scientific study of plants, known as botany, has identified about 350,000 extant species of plants, defined as seed plants, bryophytes, ferns and fern allies. As of 2004, as a main or exclusive food source[1], in many cases leaving the seeds damaged and not viable. Granivores are found across many families of vertebrates Vertebrates are members of the subphylum Vertebrata, chordates with backbones and spinal columns. About 58,000 species of vertebrates have been currently described. Vertebrata is the largest subphylum of chordates, and contains many familiar groups of large land animals. Vertebrates are comprised of animals from the groups jawless fishs, bony fish, and invertebrates An invertebrate is an animal without a backbone. The group includes 95% of all animal species — all animals except those in the chordate subphylum Vertebrata (especially mammals Mammals are a class of vertebrate, air-breathing animals whose females are characterized by the possession of mammary glands while both males and females are characterized by hair and/or fur, three middle ear bones used in hearing, and a neocortex region in the brain. Some mammals have sweat glands, but most do not, birds Birds are winged, bipedal, endothermic (warm-blooded), egg-laying, vertebrate animals. There are around 10,000 living species, making them the most varied of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from the 5 cm (2 in) Bee Hummingbird to the 2.75 m (9 ft) Ostrich and insects Insects are a class within the arthropods that have a chitinous exoskeleton, a three-part body (head, thorax, and abdomen), three pairs of jointed legs, compound eyes, and two antennae. They are among the most diverse group of animals on the planet and include more than a million described species and represent more than half of all known living) [2]; thus, seed predation occurs in virtually all ecosystems (see further readings). Seed predation is commonly divided into two distinctive temporal categories, pre-dispersal and post-dispersal predation, which may involve different strategies and requirements and have different implications at the individual and population level. Nevertheless, regardless of timing, seed predation has great implications for plant population dynamics (see below). To counterbalance effects of predation, plants have evolved defenses such as seed morphology (size, shape, toughness) and chemical defenses (secondary compounds Secondary metabolites are organic compounds that are not directly involved in the normal growth, development, or reproduction of organisms. Unlike primary metabolites, absence of secondary metabolities does not result in immediate death, but rather in long-term impairment of the organism's survivability, fecundity, or aesthetics, or perhaps in no such as tannins Tannins are astringent, bitter plant polyphenols that either bind and precipitate or shrink proteins and various other organic compounds including amino acids and alkaloids. The astringency from the tannins is what causes the dry and puckery feeling in the mouth following the consumption of unripened fruit or red wine. Likewise, the destruction or and alkaloids Alkaloids are a group of naturally occurring chemical compounds which mostly contain basic nitrogen atoms. This group also includes some related compounds with neutral and even weakly acidic properties. Also some synthetic compounds of similar structure are attributed to alkaloids. Beside carbon, hydrogen and nitrogen, molecules of alkaloids may) to defend against their seed predators (see below). However, as plants have adapted defenses to seed predation (e.g., chemical compounds), so have seed predators adapted to plant defenses (e.g., ability to detoxify chemical compounds). Thus, many interesting examples of coevolution In a broad sense, biological coevolution is "the change of a biological object triggered by the change of a related object". Coevolution can occur at multiple levels of biology: it can be as microscopic as correlated mutations between amino acids in a protein, or as macroscopic as covarying traits between different species in an arise from this dynamic relationship.
Strawberry The garden strawberry is a common plant of the genus Fragaria cultivated worldwide for its aggregate accessory fruit, the strawberry. The fruit is widely appreciated, mainly for its characteristic aroma but also for its bright red color, and it is consumed in large quantities, either fresh or in prepared foods such as preserves, fruit juice, pies, fruit damaged by a mouse A mouse is a small mammal belonging to the order of rodents. The best known mouse species is the common house mouse (Mus musculus). It is also a popular pet. In some places, certain kinds of field mice are also common. This rodent is eaten by large birds such as hawks and eagles. They are known to invade homes for food and occasionally shelter eating the seeds
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Seeds and their defenses
Plant seeds are important sources of nutrition for animals across most ecosystems. Seeds contain food storage organs (e.g., endosperm Endosperm is the tissue produced under the seeds of most flowering plants around the time of fertilization. It surrounds the embryo and provides nutrition in the form of starch, though it can also contain oils and protein. This makes endosperm an important source of nutrition in human diet. For example, wheat endosperm is ground into flour for) that provide nutrients to the developing plant embryo (cotyledon). This makes seeds an attractive food source for animals because they are a highly concentrated and localized nutrient source in relation to other plant parts.
Seeds of many plants have evolved a variety of defenses to deter predation from seed predators. Plants may allocate resources toward physical or chemical defenses. Seeds are often contained inside protective structures or fruit pulp that encapsulate seeds until they are ripe. Other physical defenses include spines, hairs, fibrous seed coats and hard endosperm.
Some seeds have evolved strong anti-herbivore chemical compounds. In contrast to physical defenses, chemical defenses in seeds to deter consumption by seed predators by using chemicals that are toxic to granivores or inhibit the digestibility of the seed. These chemicals include non-protein amino acids, cyanogenic-gycosides, protease and amylase inhibitors, Phytohaemaglutinins [3]. Seeds face trade-offs between allocation toward defenses and the size and number of seeds produced. Additionally plants have trade-offs in seed defense allocation between deterring seed predators and attracting seed dispersers.
Plants may reduce the severity of seed predation by making seeds spatially or temporally scarce to granivores. Seed dispersal away from the parent plant is hypothesized to reduce the severity seed predation (see below for further details) [4] [5] Seed masting is an example of how plant populations are able to temporally regulate the severity of seed predation. Masting refers to a concerted abundance of seed production followed by a period of paucity. This strategy has the potential to regulate the size of the population of seed predators.
Pre- vs. post-dispersal seed predation
Seed predation can often occur at two different stages. Pre-dispersal seed predation occurs when seeds are consumed while still on the plant, thus being concentrated and very conspicuous. Conversely, post-dispersal seed predation occurs when seeds are consumed after being released by the parent plant (i.e., dispersed), thus being at low densities, scattered and/or hidden in the environment.
Both pre- and post-dispersal seed predation are extremely frequent in nature. However, fundamental differences occur between the two. Pre-dispersal predators are most often specialists, as they are more likely to adapt to clustered resources. Predator specialization requires that these animals utilize specific cues like plant chemistry (volatile compounds), color and size to attack seeds. In addition, specialization requires that the life cycle of the predator match the production of seeds by the host plant. Therefore, animals with shorter life span, like insects, are more common pre-dispersal predators. Common insect groups of pre-dispersal predators are Coleoptera, Hemiptera, Hymenoptera and Lepidoptera. For this reason, a greater diversity of predators feed on seeds prior to dispersal [6]. Nevertheless, there are important vertebrate pre-dispersal predators, especially birds and small mammals.
Post-dispersal seed predation is extremely common in virtually all ecosystems. Given the heterogeneity in both resource type (seeds from different species are available), quality (seeds of different ages and/or different status of integrity or decomposition) and location (seeds are scattered and hidden in the environment), most post-dispersal predators have generalist habits [7]. These predators usually belong to a diverse array of animals, such as ants, beetles, crabs, fish, rodents and birds. In addition, not only is the assemblage of post-dispersal seed predators diverse, but its composition varies considerably among ecosystems [8].
The severity of predation rates also varies between pre- and post-dispersal predation. Although both types of predation can be extremely high, studies simultaneously evaluating both pre- and post-dispersal seed predation suggest that the latter is often more severe than the former [9]. However, seeds already dispersed and not consumed have a chance to germinate, and seeds consumed could die regardless of predation due to constraints imposed by unsuitable germination sites. On the other hand, all non-dispersed seeds predated would be no more than a waste of energy by the parent plant. Therefore, the demographic impacts of pre-dispersal predation on plant populations are likely to be stronger than the impacts of post-dispersal predation.
Effects on plant demography
The complex relationship between seed predation and plant demography is an important topic of plant-animal interactive studies. Plant population structure and size over time is closely associated with the effectiveness at which seed predators locate, consume, and disperse seeds. In many cases this relationship is dependent upon the type of seed predator (specialist vs. generalist) or the particular habitat in which the interaction is taking place. The role of seed predation on plant demography may be either detrimental or in particular cases actually beneficial to plant populations.
The Janzen-Connell model [10] [11] is one of the most important studies of how seed predation may influence plant demography. The Janzen-Connell model illustrates how seed density and survival respond to distance from the parent tree and differential rates of seed predation. Seed density is hypothesized to decrease as distance from the parent tree increases. Where seeds are most abundant under the parent tree, seed predation is predicted to be at its highest. As distance from the parent tree increases, seed abundance and thus seed predation are predicted to decrease as seed survival increases.
The degree to which seed predation influences plant populations may vary by whether a plant species is safe site limited or seed limited. If a population is safe site limited it is likely that seed predation will have little impact to the success of the population. In safe site limited populations increased seed abundance does not translate into increased seedling recruitment. However, if a population is seed limited, seed predation has a better chance of negatively affecting the plant population by decreasing seedling recruitment. A study by Maron and Simms [12] found both safe site limited and seed limited populations depending on the habitat in which the seed predation was taking place. In dune habitats seed predators (Deer mice) were limiting seedling recruitment in the population, thus negatively affecting the population. However, in grassland habitat the seed predator had little effect on the plant population because it was safe site limited.
In many cases seed predators support plant populations by dispersing seeds away from the parent plant. By dispersing seeds away from the parent plant the seed predator is in effect supporting gene flow between populations. Other seed predators collect seeds and then store or cache them for later consumption [13]. In the case that the seed predator is unable to locate the buried or hidden seed there is a chance that it will later germinate and grow, supporting the species dispersal.
See also
- Herbivory Herbivores are animals that are adapted to eat plants. Herbivory is a form of predation in which an organism consumes principally autotrophs[page needed] such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in general are known as primary consumers
- Seed dispersal Seed dispersal is the movement or transport of seeds away from the parent plant. Plants have limited mobility and consequently rely upon a variety of dispersal vectors to transport their propagules, including both abiotic and biotic vectors. Seeds can be dispersed away from the parent plant individually or collectively, as well as dispersed in
References
- ^ Hulme, P.E. and Benkman, C.W. (2002) Granivory. In Plant-animal Interactions: An Evolutionary Approach, ed. C.M. Herrera and O. Pellmyr. Oxford: Blackwell.
- ^ Janzen, D.H. (1971) Seed predation by animals. Annual Review of Ecology and Systematics, 2, 465-492.
- ^ (Herrera and Pellmyr 2002)
- ^ Janzen, D.H. (1970) Herbivores and the number of tree species in tropical foresets. American Naturalist, 102, 592-595.
- ^ Connell, J.H. (1971) On the role of natural enemies in preventing competitive excusion in some marine animals and in rainforest trees. In Dynamics of Populations, ed. P.J. den Boer and G.R. Gradwell. Wageningen: Center for Agricultural Publishing and Documentation, pp. 298-312..
- ^ (Hulme and Benkman 2002)
- ^ (Hulme and Benkman 2002)
- ^ (Hulme and Benkman 2002)
- ^ (Hulme and Benkman 2002)
- ^ Janzen, D.H. (1970) Herbivores and the number of tree species in tropical foresets. American Naturalist, 102, 592-595.
- ^ Connell, J.H. (1971) On the role of natural enemies in preventing competitive excusion in some marine animals and in rainforest trees. In Dynamics of Populations, ed. P.J. den Boer and G.R. Gradwell. Wageningen: Center for Agricultural Publishing and Documentation, pp. 298-312..
- ^ Maron, J.L. and Simms, E.L. (1997) Effects of seed predation on seed bank size and seedling recruitment of bush lupine (Lupinus arboreus). Oecologia ,111,76-83.
- ^ Harper, J.L. (1977) Population Biology of Plants, New York: Academic Press.
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Nighthawks, like meadowlarks, nest on the ground in open situations, where their young are particularly susceptible to fire ant predation . ...
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Modeling efforts at ISU have shown that seed predation can significantly affect long term weed population dynamics within agricultural fields For example in a 4 year crop rotation corn
